The present invention relates to a process for recovering metal values from based alloy scraps based on Ni, Co, or both and especially superalloy scraps but also high alloy chromium bearing and corrosion resisting alloy scraps with considerable amounts of valuable metals. The scrap is becoming increasingly contaminated nowadays because of the higher content of alloys and other tramp elements. The utility value of such scraps can be considerably increased by separating the valuable metals into marketable, technically useful products.
Nickel and cobalt based superalloys typically contain about 50 to 70 percent nickel and/or cobalt, 15 to 30 percent chromium, and the balance is made up of molybdenum, tungsten, columbium, titanium, aluminum, iron, manganese, silicon, and carbon. Contaminating metals may include copper, lead, zinc, and tin. Other contaminants include oil, moisture, rags, wood, earth, and corundum grinding debris.
Alloy scraps in the following forms are suitable for refining: turnings, catalysts, uprunnings, grindings, sludges, muds, spills, off-grade multi-metals and ingots. Powder metallurgical products are normally not suitable. Table 1 gives the analyses of some typical superalloy scraps.
TABLE 1 ______________________________________ Analysis of typical superalloy scraps Average Normal limits Analysis % % ______________________________________ Ni 39.3 1.5-63 Co 21.2 7-56 Cr 17.0 8-32 Mo 3.9 2-10 Ti 1.8 0.3-5 Al 1.7 0.1-6 W 2.6 1-17.5 Cu 0.02 0.05-0.5 Ta 0.41 4.25-9 V 0.03 0.01-1.0 ______________________________________
The recovery of metal values from the superalloy scraps contemplated herein has been tested so far mainly by using hydro- and pyrometallurgical methods.
The hydrometallurgical leaching and chemical purification methods are successful only with scrap in fine form like drillings, turnings, etc. Leaching of scrap in big pieces is slow, and is possibly only by the heap leaching method on an industrial scale. This will not be practical for a long time.
In order to speed up the leaching, metallic superalloy scrap can be carborized at melting temperatures, and after cooling be crushed and ground after which it can be selectively leached so that the metals to be recovered can be hydrometallurgically refined by well-known methods.
Better results from the practical and economic point of view have been obtained by pyrometallurgical smelting methods in controlled conditions, but the practical industrial applications are very rare and they have been only partly successful.
The object of the present invention is to provide a process for refining the metal alloy product scraps to produce Ni/Co-alloys with the required purities and to recover the middle products for further purification by e.g. well-known metallurgical and chemical methods choosing the most suitable one for each type of slag.